1. Field of the Invention
The present invention relates to a method and apparatus for performing intra prediction type decoding on digital video data that has been encoded using an intra prediction type prediction mode. The present invention also relates to a method and apparatus for providing the proper signaling to a decoding unit for informing the decoding unit as to the proper intra prediction mode to apply.
2. Discussion of the Related Art
Generally there are two methods for accomplishing video data compression in order to eliminate temporal and spatial redundancy found amongst video data. Eliminating temporal and spatial redundancy is an important requirement to increase a compression ratio for the video data, which in turn will decrease an overall video data size for later storage or transmission.
An inter prediction encoding method is able to predict a current video data block based on similar regions found on a previously encoded picture of video data that precedes a current picture that includes the current video data block. And an intra prediction encoding method is able to predict a current video data block based on previously encoded blocks that are adjacent to the current video data block and within a same picture. The inter prediction method is referred to as a temporal prediction method, and the intra prediction method is referred to as a spatial prediction method.
An encoding unit is able to take an original RGB video signal and encode it into digital video data that serves as a digital representation of the original RGB video signal. By processing both the inter and intra predictions on the original RGB video signal, the encoding unit is able to create an accurate digital video representation of the original RGB video signal. Each block of digital video data that is prediction processed is referred to as a prediction unit. Depending on whether a prediction unit was processed according to an intra prediction mode or inter prediction mode, the prediction unit may come in a variety of available block sizes. Once the encoding unit has encoded all of the original RGB video signal into corresponding prediction units of digital video data, the resulting digital video data may be transmitted to a decoding unit for decoding and reproduction of the original RGB video signal. In order for the receiving decoding unit to reproduce an accurate reproduction of the original RGB video signal, the decoding unit must perform the same prediction mode processing on a prediction unit as was used at the encoding unit.
Pertaining specifically to the intra prediction method for prediction processing a prediction unit of digital video data, there exists various intra prediction modes known today for accomplishing the spatial prediction that defines the intra prediction method. Yet even with the various intra prediction modes currently available, there is always the need to update existing intra prediction modes and to offer new intra prediction modes in order to accomplish more accurate predictions.
When increasing the total number of intra prediction modes available for intra predicting a prediction unit, there is the often-times overlooked consequence of increasing a maximum binary codeword length that is needed to identify each of the available intra prediction modes. As noted above, when the encoding unit performs prediction processing on a prediction unit according to a specific intra prediction mode, the decoding unit must then perform prediction processing on the prediction unit according to the same specific intra prediction mode to ensure accurate reproduction of the original RGB video signal. The only way to notify a decoding unit as to which specific intra prediction mode was used to predict the particular prediction unit at the encoding unit is to attach intra prediction mode identifying information to each prediction unit. This is an undesirable consequence of offering new intra prediction modes. This way, the decoding unit can parse the intra prediction mode identifying information and determine the proper intra prediction mode to process on a particular prediction unit.
This being said, each intra prediction mode identifying information will be a binary codeword comprised of ‘0’s and ‘1’ in terms of digital data. And as the number of new intra prediction modes that need to be uniquely identified increases, so too will the maximum length of the binary codeword that corresponds to the intra prediction mode identifying information. As a simple example, it may only require a maximum 3 bit long codeword to uniquely identify four unique intra prediction modes. ‘01’ can identify the first intra prediction mode, ‘10’ can identify the second intra prediction mode and ‘100’ can identify the third intra prediction mode. However by adding just two new intra prediction modes, the maximum bit length for the codewords identifying each of the intra prediction modes may grow to a maximum 4 bit long codeword. To identify the new fifth intra prediction mode the codeword ‘1001’ may be assigned, and to identify the sixth new intra prediction mode the codeword ‘1101’ may be assigned. Therefore the real cost of increasing the number of total intra prediction modes available is in the number of total digital information that must be transmitted to identify all of the new intra prediction modes. This in turn results in more and more information bits needing to be transmitted along with the actual video data bits, which obviously decreases the efficiency of the overall video signal compression.
Therefore there also exists a need to conserve a total number of informational bits transmitted with the video data by reducing the maximum bit length of the codewords assigned to identify each new intra prediction mode.